fix(coral): Remove superfluous defaultValue in TopicSchemaRequest

[mathieu-anderson]

About this change - What it does

Navigating to /topic/aivtopic1/request-schema will return this warning in the browser's console:

Warning: Select elements must be either controlled or uncontrolled (specify either the value prop, or the defaultValue prop, but not both). Decide between using a controlled or uncontrolled select element and remove one of these props. More info: https://reactjs.org/link/controlled-components

This is because we set a defaultValue for the Topic name's NativeSelect, when none is needed: its value is already set by the useForm's defaultValues option.

We can therefore safely delete it and solve the conflict.